How to test a wall thermostat to see if it's actually working?

Thanks. I've identified four safeties:
1. The lockout timer (still not sure what its specific role is)
2. The fusible link
3. The vent safety shutoff switch
4. The limit switch
Luckily, all four must be working fine, since the heat is on!
Woo hoo!

Nope. Now the blower doesn't go on at all when I hold down the furnace door
switch. I did hear some snapping at one point, but then it went away.
It was like a sharp click click click...
So I opened the blower door (to interrupt the power) and gently tapped on
everything, especially the solenoids; and I wiggled all the wires. I found
one that seemed loose; and now it's back on tightly...

Wow. I tried this just now, in the dark, and, for a short while, everything was
working again!
The click click click I had heard was a snapping sound as the pilot was being
lighted. Soon, the pilot light lit!

http://farm3.staticflickr.com/2845/11318356605_a78bf71569_o.gif
Then, after about a minute (I didn't measure it), the entire burner was aflame!

http://farm8.staticflickr.com/7397/11318411966_be80c6d243_o.gif
And, within another while (again, I didn't think to measure), the blower ran!

http://farm8.staticflickr.com/7427/11318411706_f7ceb36cd5_o.gif
I accidentally hit the door switch while I was trying to measure voltages,
so the whole thing shut down - and I couldn't reproduce the success - but -
I'll try again tomorrow when I have more light to work with (and it will
be warmer besides, as it's going to be at freezing tonight).

Hi,
Leave that door open for now and tape down the switch. You may have a
intermittent ignitor. This is the one like BBQ lighter. When you hear
zapzap sound, you should be able to see spark. Remove the tape and close
the cover when problem is solved. Piezo ignitor is known to go bad when
old. I used to have that problem in my 5th wheel camping trailer fridge.
Only remedy is replacing whole module.

I've been playing with it for a while, and, can't seem to fully reproduce
my success. I'm going to hit the sack and attack it again in the daylight.
Seems to me all those *timers* are making a clean starting point difficult,
particularly the thing called a "lockout timer"...

http://farm6.staticflickr.com/5518/11312983254_ab27d0a8ef_o.gif
I'm starting to wonder if it's a bad thing that the wife loves to turn the
thermostat off and on constantly all day, as if *she* is the automatic
control!

That 'stat is old work horse using wet mercury bulb switch. It is
tilting up/down by temp. sensitive bimetal coil. Just leave it at about
75 deg during trouble shooting(to make it call for heat) Leave it alone
and adjust it when problem is fixed.
Don't worry about lock up timer it only starts when safety issue arises
like over heating triggering over heat limit sensor. This is
kind of thermostat for fixed temp sensing. There are few in there for
different functions/purposes. If you want to reset the lock out timer
just power cycle the furnace,(resetting control board) Hope it is not
cold there. It is -18C up here tonight.
You in Silicon valley? In San Jose area? There I have a good friend of
mine who runs company called K.Y. systems. His back is EE like me.
He may may not help you if you call him and mention my name,
Tony(VE6CGX). His name is Young Kim. He goes out of country often on
business.

Just as an aside, the $279 lockout timer appears to be a normally open
switch, based on these two descriptions:
http://www.furnacepartsource.com/dls015.html
https://acpartsdistributors.com/index.php?main_page=product_info&products_idY920
It is called a "Combustion Safety Control Lockout Timer" (whatever that
is supposed to mean) over here, also sold for $279:
http://www.bestbuyheatingandairconditioning.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=CIB72CH003&Category_Code=r-lockout
So, it seems to be an expensive normally opened timed switch.
It seems to have a timer of about five minutes.
After five minutes, presumably it closes the SPST switch.
I'm still trying to figure out what it's supposed to do.
It's hooked up *before* the pilot, so, being normally open is
odd.
http://technicalhotandcoldparts.com/carrier-hh72ch003-lockout-timer-control.html

I don't understand *what* it does yet.
Sure, it's called a "lockout timer", so it locks out the gas, I guess.
But, how does it figure out when/if to lock out?
All I can tell, so far, is that it's a normally open SPST switch.
http://www.lennoxproducts.com/wp-content/uploads/2012/05/HH72CH003.pdf

It seems that only the propane retrofits have this lockout timer.
Apparently, the heaters are originally made for LPG.
When they're converted to Propane, they apparently add the lockout timer.
Apparently propane gas has qualities that require that lockout timer
so that the gas is evacuated from the passageways.
That's all I know, so far (or think I know).

They were made for natural gas, which is lighter than air and
dissipates in event of accidental release, while propane (lpg) is
heavier than air and settles in the low spots - so the lockout timer
is used to prevent ignition before the possible accumulated gas is
dissipated.

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